Take-off computer



3 Sheets-Sheet l Jan. 7, 1964 c. B. BRAHM Y TAKE-OFF COMPUTER Filed Jan. e, 1959 Jan. 7, 1964 c. B. BRAHM TAKE-OFF COMPUTER 5 Sheets-Sheet 2 Filed Jan. 6, 1959 /U/ a7 Afa/ 453373795 CHARLES BRA/1M 5,02/ m Arron/vw Jan. 7, 1964 c. B. BRAHM TAKE-OFF COMPUTER Y Filed Jan. e, 1959 3- Sheets-Sheet 3 TTORNEV United States Patent 3,116,638 TAKE-GFF CMPUTER Charitas E. Brahim, Eilington, Conn., assigner to United Aircraft Corporation, East Hartford, Conn., a corporation of Deiaware Filed lian. 6, 1959, Ser. No. 735,172 8 Claims. (Ci. 73-178) This invention relates to airplane take-off safety and more particularly to the teaching of an aircraft takeoff monitor.

ln the age of jet aircraft, a number of problems have arisen not previously troublesome with propeller-driven pianes, Among these problem areas have been the hazards and uncertainties of take-off. lt is important that falsely aborted take-offs should be avoided from a safety, economy and operations standpoint and it is equally as important that the pilot be warned as early as possible in takeoff roll whether, under the present airplane and climatic conditions, the airplane Iwill be airborne at takeoff point. if the airplane is incapable of proper take-off under these conditions, the pilot should begin his braking lattempts as early as possible.

it is an object of this invention to provide mechanism which will advise the aircraft pilot early in `the take-off roll whether the aircraft will be airborne at the runway takeoff point.

It is a further object of this invention to teach an airplane take-off monitor in which the present aircraft velocity (Vp) is ascertained early in the take-off roll and continuously thereafter, then differentiated into aircraft acceleration, which acceleration is multiplied by the time remaining (Tr) or the distance remaining (DR) to the runway take-off point to provide a product, which product and present velocity (Vp) are added and compared to the calculated take-off velocity (VTO), required lift or aircraft Weight to ascertain early in the aircraft take-ofi roll and continuously thereafter whether the airplane will be airborne at take-olf point.

Other objects and advantages will be apparent from the specification and claims, and from the accompanying drawings which illustrate an embodiment of the invention.

FllG. 1 represents a block diagram of my take-off monitor.

FIG. 2 is an electrical diagram showing my initiation circuit.

FiG. 3 is an electrical diagram illustrating my take-off monitor.

FIG. 4 is an electrical schematic showing compensation for airplane flap angle.

FIG. 5 is a graphic representation of the effect of multiplying the acceleration signal by time remaining to the take-off point to obtain a predicted future velocity signal.

My take-off monitor has been designed so that it will calculate early in take-off roll a predicted aircraft lift or aircraft velocity at the runway take-off point, based upon airplane and climatic conditions, for example, aircraft gross `weivht, assisted take-off, flap angle, runway gradient and surface conditions, altitude, dew point, and air temperature, and compare same to the manually calculated lift required to overcome aircraft weight or to the aircraft take-off velocity (VTO) which will be necessary to permit take-off at take-off point. The mathematical derivation of the equation which will be `used by my take-off monitor will now -be fully explained.

ICG

The lift available from an aircraft is given by the equation:

:AGIP

L=lift A=elfective wing area C1=coeflicient of lift at the maximum angle of attack to be used at takeoff pzair density Vpzaircraft ground velocity VW-:wind velocity parallel with aircraft At take-off, the lift must at least equal the weight (W) of the aircraft, so that, at take-off,

The difference etween static and total pressure (AP) at the front of the aircraft is:

(Equation 2) lf a pressure transducer is used to convert the pressure difference, Al), into a voltage E, which is proportional to the square root of AP, the following relationships are established:

(Equation 4) E=KVAP (Equation 7) T d V p q.- V /D 1 Vw PW Trm take-on veloolty To) From the lift equation previously developed, Equation (2), we know that the air speed at take-off must be greater than a value obtained by transposing in Equation 2, so that:

The time (To) required to make the take-off run will be equal to the runway length .to take-off point (X) divided by the average velocity. Since the acceleration will be essentially constant, the average velocity will be equal to one-half the final velocity, so that:

2W AGIP-.Vw

(Equation 8) Vp (Equation 9) To:

The normal wind velocity is small compared to the required air speed at take-Gif, so that variations in wind velocity will not have a large effect on the time required to complete the take-off run. The normal variation in air density and take-off weight will also have a relatively small effect on the take-off time To, since these parameters do not vary over a Wide range, and also because the take-off time is affected as a function of the square root of these parameters. While all these variables could be included in the calculation of the take-off time, it is felt that all variations other than runway length can be ignored, so that:

(Equation l) T0=K1X 2 (Equation 1l) K1: ZWWX.

ACxpo Wmaxzmaximum take-olf weight p0=standard air density (Equation 12) 7 y (Z/;"=\/2 (using Equation 6 and disregarding Vw) and the calculated air speed at the take-off point is equal to:

(Equation 13) Calculated take-olf point air spoed I( T-t) (using Equation 7) Eq uation 11i) Calculated take-olf point air speed :Tlvg [E4-@(T-] (incorporating Equation 6) 1f p (lt The required air speed has previously been calculated to be equal to:

(Equation l5) V (soo E nation 8) D 1)/[1 AC1 q When the calculated air speed is equal to the required air speed, the take-off is just possible, and

(Equation 16) calculated required air speed air speed KJ; di( 5%/ ACI 4 V- 4 E f W (Equation 17) E-ldt (T L/ or, since E is proportional to Vp,

dt AC1 Since the right hand side of Equation 18 is representative of the airplane speed or velocity necessary for takeoff, as calculated in Equations 8 and 16, it will be referred to as take-off velocity (VTO) (Equation 18) V-I (Equation 19) and the term dV-U CZVD (Equation 20) dt (T dt Tr V (Equation 21) VD+V=VTO which states that the present velocity of the aircraft plus the velocity which will be gained by reason of present acceleration must equal or exceed the velocity necessary for the aircraft to take `off if a successful take-off is -to be made.

When the left side of Equation 18 or 2l is larger than the right side, the take-oit run is proceeding satisfactorily. When the left side is the smaller of the two, the take-off attempt must be stopped.

in the fashion now to be described, my take-off monitor is used to derive the calculated air speed or left side of Equation 18, i.e.,

dv Vp+ di while the required 'air speed (VTO) or right side of Equation 18 is calculated in advance and preferably manually entered into our control panel for monitor comparison purposes.

Referring to FIG. 1 we see that airplane 10, which may be of any conventional typ-e well-known in the art, which carries therewith on its take-off run differential pressure transducer 12 which includes total pressure `tap 14 and static pressure tap 1:6 to provide a pressure differential proportional to aircraft runway velocity or present velocity (Vp) which, in accordance with Equations 4 and 17 generates voltage E. From differential pressure transducer '12, the present Velocity (Vp) signal in the form of voltage E is transmitted both through line 18 to adder 20 and also through line 22 and attenuator 24 into derivative or diiferential circuit 26, from which and through line 28 a velocity derivative signal to multiplier 30. At the saine time that the velocity derivative signal (IVD Clt is being provided to multiplier 39, a second signal known 'as runway time remaining (Tr) is also provided to multiplier 30 in the following fashion. Total runway time (To), namely the time from the beginning of take-off roll to take-off point is calculated in advance and manually entered into control panel 34 from whence it passes along line 36 into time computer 38, which is essentially a clock which commences running .at a time dictated by initiation circuit 4% in a fashion to be described hereinafter in connection with FIG, 3, and indicates elapsed time (t).

The two signals, total runway time (To) and elapsed runway time (t), are subtracted in time computer' 38 to derive remaining runway time (Tr). This remaining time signal T1r is the second sign-al which enters multiplier 30 through line 44 simultaneously with the velocity derivative signal from line 28. From multiplier 30, the future vclocity signal Vf, which is equal to di )Tf is passed through line 60 to adder 20 together with the present velocity signal Vp which is provided thereto through line 18. From adder 20 the sum of the present velocity signal Vp and the iiuture velocity signal Vf is transmit ed along line d2 to indicator @4 to be compared therewith with the Velocity calculated to` be necessary for take-oil" (VTC). This calculated take-off velocity (VTC) is calculated from the right side of lEquation 18 and is manually entered into control panel 34 as, for example, by a dial in the pilots compartment, and passes along line 66 to provide a required lair speed signal, VTO, to be compared in indicator 6d, preferably in a go-no-go visual or audible signal to indicate to the pilot whether take-olf can safely be made or should be aborted. This is the basic take-oli1 monitor, however there are preferred additions which should advantageously be made thereto and which will now be described.

FiG. 5 illustrates graphically how the future velocity signal (Vf) is computed. Assuming that acceleration is a constant, initiator circuit 4d will actuate time computer 3S after a specied delay. When this occurs, indica-ted by A on FlG. 5, time computer 38 twill vary potentiometer lo@ and eectively multiply the dVp di or Ap) signal by the dierence between the total runway time (To) and elapsed time t), which has been called time remaining (Tr). The computed time remaining (Tr) wil-l be a decreasing vlalue, so that as time passes, Tr will eventually become zero, as point B in FIG. 5. Now the present velocity (Vp) must equal the predetermined takeoft" velocity (VTC.) for the aircraft to become airborne. As time remaining (Tx.) decreases, the computed signal (Vf) will also decrease, since in :the shorter time remaining a constant acceleration will result in a smaller increase in velocity.

Further, since our aircraft will accelerate very rapidly within the -lirst few seconds of take-oil roll and then stabilize thereafter and because it is desirable to eliminate pilot start buttons, it is desirable that time computer 38 not commence running lduring taxiing but delay until a prescribed length of time has elapsed from the beginning of take-oit roll and until a given acceleration has been reached. Initiator circuit dit shown more completely in FIG. 2 accomplishes this function.

An acceleration signal, possibly from derivative circuit 216 is passed -to initiator circuit 40. Clipping diode 9d is biased to some positive voltage by resistors 120l and 122. The iunction of the clipping diode is to limit the maximum magnitude of the positive voltage and to provide a constant step signal to a time lag circuit comprising resistor 95 and capacitor 915. The integrated output of capacitor 95 will, when it builds up as determined by the time constant of the circuit, forward bias transistor 98 and allow current to iiow from source 97 through solenoid M6 and transistor 98 to ground. Energization of solenoid 12o closes switches liti@ and lll'l and permits a ilow of current to actuate time computer 318.

The constant voltage from capacitor 9e coupled with the time constant or" the integrator network provides a constant voltage output with respect to time regardless of the input acceleration. This circuit will always energize the time computer at a fixed time after take-oli is initiated, making the circuit independent of the acceleration signal.

Closing latch switch lul gives the current from source 97 an additional path to ground, so that if the acceleration signal should decay and transistor 93 is turned ott", solenoid 26 will remain energized and switch ldd will also remain closed.

lt is also considered important to advise the pilot when he passes his final refusal point on the runway so that he may take immediate braking action at that point. To accomplish this purpose, we calculate, considering the aircraft and climatic conditions, the time oit refusal (Tref) from initial take-oil until this refusal point will be reached and put such a signal into control panel 34 from which'it is fed through line 110 to adder 112 which also receives from line 42 a time remaining (T1.) signal. Adder 112 gives the pilot either visible or audible warning when the difference between time of refusal (Tref) and time remaining (Tr) reaches a preselected minimum ligure to permit reaction time and effective braking of the airplane within runway length.

FG. 3 illustrates the electrical circuitry for my takeotl" monitor. Reference numerals corresponding to those used in the description of FG. l will be used whereever applicable. The present velocity Vp signal from air speed pressure transducer 12 is passed through line l and also through derivative circuit 26 so that the DC. signal d dt is provided to modulator 15d from whence it passes to amplifier 52 as an AC. signal. The AC. signal from amplier 152 passes through two paths. The first of these paths is through demodulator 154 from whence it is passed as a DJG. signal to trigger initiator circuit 4t), explained more fully in connection with FG. 2. The initiator circuit, as fully explained with the description of FIG. l starts the clock mechanism of time computer 38 running. From any convenient source such as control panel 3f.'- of FIG. l, total take-oil time To is fed into time computer 33 to have elapsed time (t) subtracted therefrom so that runway time remaining (T1.) is passed from time computer 38 to an adder ld, which also receives computed refusal time (Tm.) from member le@ and subtracts ltime remaining (Tr) therefrom to provide the pilot with a signal announcing the approach of the refusal point, which is the last opportunity for the pilot to successfully abort the take-oliC attempt and commence braking operation. From time computer 38, a time remaining signal (Tr) also passes to an electrical multiplier, for example by movement ot the wiper of potentiometer 162, where the AC. signal is multiplied by the time remaining signal (Tr). potentiometer i162 the AC. signal dt r which is equal to the predicted nal velocity Vf passes to amplier loe and is then changed to DC. in dernodulator 166.

Both the Vf signal in line e@ and the present velocity signal, V in line 13 are passed through resistors, ld and '7tl, much larger than the resistance of indicator ed, to provide a constant current input which is added to form a resultant current proportional to tne predicted aircraft velocity at the take-oit" point. The combined signal Vp-l-Vf flows into one side of indicator ed. Takeoli velocity VTO is passed as a current to indicator d4 from the opposite direction through line e6. indicator 64 can be a milliarnmeter, and summation of the actual aircraft velocity current, the product of acceleration time remaining current, and the required take-oli velocity current will deflect the meter in a direction indiI tive of the actual aircraft condition. A negative indication causes the meter to deflect into the Stop region, thereby indicating an inability to take-oli. Positive current indicates that the predicted velocity at take-oil time will be greater than the required take-oil velocity, thereby causing the meter to be deflected into the Go region. The prominent feature of this type of adder is that there is a negligible interaction between the signal, and it provides for a more linear type of signal addition, eliminating the need for non-linear calibration 01"' the indicating instrument. The indicator, however, may also be an audio instrument or any instrument which will provide Fron 7 vthe pilot with a continuous signal indicating whether or 'not the airplane is capable of being airborne at take-off point.

The take-off velocity signal passed by line 66 is indicated in FIG. 3 as being generated by a manually adjusted potentiometer 174. Because the velocity necessary fo take-off is a variable dependent on many parameters such as aircraft weight and iap angle, it is possible to manually compute the take-off velocity beforehand. It can be provided, however, that circuitry will perform some of the desired computations. For example, in FlG. 4 a simple circuit is shown in which the Wiper arm of potentiometer 175 is varied as a function of ap angle, either continuously or as a multiple position switch arrangement. The flap angle signal is ainplied by the emitter follower circuit including7 transistor f77 and passed through potentiometer T174 where the wiper arm which picls off the voltage to be sent to indicator 64 is varied by a talle-off velocity computed without including flap angle. rfhus, for every flap angle position, a new take-olf velocity signal will be sent to indicator 64.

Another feature which may be incorporated to assist in computing take-olf velocity is a fuel totalizer. At times an aircraft will be held up before take-off, and will consume a considerable amount of fuel while waiting. The gross weight of the aircraft will decrease as fuel is consumed, and the lift needed for take-olf is correspondingly reduced. A device such as a fuel totalizer can be utilized to sense the amount of fuel consumed or remaining and vary a potentiometer, such as that of numeral 175 of FIG. 4, and indicate that a change in aircraft weight has taken place. Obviously both aircraft weight and flap angle could be sensed simultaneously and utilized to vary the indicated take-off velocity signal which is sent to indicator 6ft.

While a preferred embodiment of the invention is shown for illustration purposes, it will be obvious to those skilled in the art that many deviations may be made therefrom without departing7 from the scope of the invention.

I claim:

l. Apparatus to ascertain early in airplane take-off roll whether the airplane will be airborne at take-oli point comprising means to ascertain airplane ground velocity,

leans to determine remaining runway time means to convert said velocity to acceleration and multiply said acceleration by said remmning runway time to obtain a product, means to add said product and said velocity to obtain a calculated take-off point velocity, and signal means to compare lsaid tie-off point velocity to required airplane velocity for take-olf.

2. Apparatus to ascertain early in airplane take-off roll whether the airplane will be airborne at take-off point comprising means to calculate predicted airplane velocity at runway take-olf point based upon early take-olf roll airplane and atmospheric conditions, and signal means to compare said predicted velocity with required airplane velocity for take-off.

3. Apparatus to ascertain early in airplane take-off roll 'whether the airplane will be airborne at take-off point comprising a differential pressure transducer having a Pilot and a static pressure tap to ascertain airplane ground velocity, an electrical differential circuit to convert said velocity to acceleration, means to ascertain remaining runway time, an electrical multiplier to multiply said acceleration by said remaining runway time to obtain a product, electrical means to add said product and said velocity to obtain a calculated take-off point velocity, and electrical signal comparison means to compare said take-olf point velocity to required airplane velocity for take-olf.

4. Apparatus to ascertain early in airplane take-olf roll whether the airplane will be airborne at take-olf point comprising means to ascertain airplane ground vclocit, means to determine remaining runway time means to convert said velocity to acceleration and multiply said acceleration oy said remaining runway time to obtain a product, means to add said product and said velocity to obtain a calculated take-off point velocity, signal means to compare said take-olf point velocity to required airplane velocity for take-oil, and means to prevent the actuation of said apparatus until a preselected aceleration is maintained for a preselected period of time.

5. Apparatus to ascertain early in airplane take-olf roll whether the airplane will be airborne at take-olf point comprising means to ascertain airplane ground velocity, means to determine remaining runway time means to convert said velocity to acceleration and multiply said acceleration by said remaining runway time to obtain a product, means to add said product and said velocity to obtain a calculated take-off point velocity, signal means to compare said take-oil point velocity to required airplane velocity for take-off, and means to compare takeoff refusal time to said remaining runway time.

6. Apparatus to ascertain early in aircraft runway roll whether the aircraft will be airborne at take-off point comprising means to pro-vide a present aircraft velocity signal, means to provide an aircraft acceleration signal, an initiator circuit connected to and responsive to said acceleration signal, a time computer connected to and triggered by said initiator circuit to provide an elapsed time signal after said `acceleration signal has attained a preselected intensity for a period of time, means to provide a total aircraft runway time signal to said time computer, means to subtract said elapsed time signal from said total aircraft runway time signal to provide a remaining runway time signal, means to multiply said remaining runway time signal by said acceleration signal to provide a product, means to amplfy said product, means to add said product to said present aircraft velocity signal to obtain a sum, means to provide a required aircraft velocity for take-off signal, and means comparing said required aircraft velocity for take-off signal and said sum.

7. Apparatus to ascertain early in airplane take-ofi roll whether the airplane will be airborne at take-off point comprising means .to ascertain airplane ground velocity, means connected to said airplane ground velocity ascertaining means to predict airplane take-off point velocity, and signal means to compare said predicted take-olf point velocity to required airplane velocity for take-off.

8. Apparatus for determining early in aircraft take-off roll ywhether the aircraft will be airborne at take-olf point including means for predicting aircraft velocity at takeolf point, means for imparting a signal to said apparatus of the velocity required for aircraft take-olf, means for modifying said signal in response to changes of the aircraft flap angle, and means for continually comparing said modified required velocity signal with said predicted aircraft velocity at take-olf point.

References Cited in the tile of this patent UNITED STATES PATENTS 2,579,902 Carbonara et al Dec. 25, 1951 2,807,165 Kuzyk et al Sept. 24, 1957 2,816,724 Snodgrass Dec. 17, 1957 2,922,982 Hoekstra Ian. 26, 1960 OTHER REFERENCES Klass: Monitor Designed To Aid l et Takeolfs, Aviation Week Magazine, June 23, 1958, pages 65, 67, 69, 7() and 7l.

Publication, Takeoff Monitors Compete for Market, Aviation Week Magazine, July 28, 1958, pages 77-79.

Morris et al.: NACA Technical Note 3252, November 1954, 19 pages.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 1169638 January 7, 1964 Charles B Brahm It is hereb eni'l requiring co Corrected below.

y certified that err or appears in the rrection and that th above numbered pate said Letters Pat ent should read as Column 'y linie 63, for "Pilot" column 8Y line 36, f

read w ptot or "amplfy" read amplify Signed and sealed this 16th day of June 19641 (SEAL) Attest:

ERNEST W. SWIDER Attesting Officer EDWARD J. BRENNER Commissioner of Patents 

7. APPARATUS TO ASCERTAIN EARLY IN AIRPLANE TAKE-OFF ROLL WHETHER THE AIRPLANE WILL BE AIRBORNE AT TAKE-OFF POINT COMPRISING MEANS TO ASCERTAIN AIRPLANE GROUND VELOCITY. MEANS CONNECTED TO SAID AIRPLANE GROUND VELOCITY ASCERTAINING MEANS TO PREDICT AIRPLANE TAKE-OFF POINT VELOCITY, AND SIGNAL MEANS TO COMPARE SAID PREDICTED TAKE-OFF POINT VELOCITY TO REQUIRE VELOCITY FOR TAKE-OFF. 